Hepatitis E virus (HEV), the causative agent of human hepatitis E, is an important public health problem in developing countries, and is also endemic in the United States and other industrialized countries. The mortality rate associated with HEV infection is up to 28% in pregnant women. Due to the lack of a cell culture and a practical animal model system, the mechanisms of HEV replication and pathogenesis are poorly understood and a vaccine against hepatitis E is still not available. Our recent discoveries of swine and avian hepatitis E viruses from pigs and chickens and the demonstrated abilities of cross-species infections by the animal HEV strains have opened up new avenues for HEV research. Hepatitis E now is a recognized zoonotic disease, and pigs (and maybe other animal species) are known reservoirs. This proposal is based on our recent discoveries of swine and avian HEVs, establishment of pig and chicken models for HEV, construction of infectious cDNA clones of human, swine and avian HEVs, and identification of cell lines supporting HEV replication resulting from two prior NIH awards on HEV (AI01653, AI46505) which have now expired. The PI decided not to submit competing renewals so that he can combine the directions of the expired awards and expand the scope of his HEV research by submitting a single new proposal. The long-term objectives are to understand the mechanisms of HEV replication, pathogenesis and cross-species infection by using pigs, chickens and non-human primates as models, and by using avian-swine, avian-human and swine-human HEV chimeras to identify genomic regions that are functionally important for these processes. In this proposal, we aim to: (1). Determining the role(s) of the hypervariable region (HVR) in HEV replication and pathogenesis;(2). Understand the molecular basis of HEV cross-species infection and host susceptibility;and (3). Fine-map the amino acid residue(s) on HEV capsid protein that are important for HEV attenuation. This will be accomplished by using standard techniques including cell cultures, molecular biology, and animal studies. The proposed studies will significantly advance our understanding of the mechanisms of HEV replication, pathogenesis and cross- species infection, and will provide useful information for future vaccine development. PUBLIC HEALTH RELEVANCE: The lack of knowledge on HEV basic biology and pathogenesis has greatly hindered the development of a vaccine against HEV. The information gained from this project will help understand the mechanisms of HEV replication and pathogenesis, and help devise effective preventive and control strategies (such as a live-attenuated vaccine) against this important but extremely understudied human pathogen.